1. Field of the invention
The present invention relates to a suspension system for anchoring wheels which are used for steering and also for driving to a frame of a vehicle.
2. Description of the prior art
Hereinafter, a fore to aft direction of the vehicle is called a "longitudinal" direction, and a side to side direction of the vehicle is called a "transverse" direction. Also, a location near a centerline of the vehicle is called an "inside" location and a location distant from a centerline of the vehicle is called an "outside" location.
There has been known a double pivot type suspension system for a vehicle. For example, Japanese Utility Model Laid-Open Publication No. 64-26507 shows such a type of suspension system. This type of suspension system comprises a steering knuckle for supporting a wheel, and an upper arm and a lower arm, respectively, connecting an upper portion and a lower portion of the steering knuckle to a frame of a vehicle. At least one of the arms comprises two link members, each of which is pivotally connected to the frame at a respective one end thereof, and to the steering knuckle at a respective opposite end thereof.
In this type of suspension system, a kingpin axis, which is an axis around which a wheel used for steering is turned, extends through a cross point between the axis of the two link members. The kingpin axis moves in response to the movement of the cross point in a horizontal plane during steering of the vehicle. A transverse distance between the kingpin axis and the center of the wheel is generally set at a positive value. In other words, the kingpin axis is located inside of the wheel center in a transverse direction.
In a FF ( front-engine-front-drive ) vehicle, when the vehicle is accelerated when it is being turned, a front wheel, which is located radially outwardly in relation to a turning circle, is provided with a momentum by a driving force acting on the wheel, so that the front wheel is pivoted toward the turning direction around the kingpin axis. Thus, the vehicle is excessively turned, which decreases the stability of the vehicle.